1. Field of the Invention
This invention relates to a semiconductor device that contains zero- or one-dimensional carrier gases, and its fabrication method.
2. Background of the Invention
In a super thin film structure or one-dimensional quantum well structure, the dimensions may be equal to the de Broglie wavelength of a conduction electron. The super thin film structure may be fabricated by depositing different types of semiconducting thin-film materials in alternation, various physical properties that have not been seen in most previous semiconductors are being found. In a one-dimensional quantum well structure, a carrier that is an electron or a hole has two degrees of freedom and is called a two-dimensional carrier gas. The one-dimensional quantum well structure has also been applied to electronic devices, such as the semiconductor laser and the high electron mobility transistor, and has begun to exert a strong influence on industry.
The multidimensional quantum well structure has also been widely studied recently. In a two-dimensional quantum well structure (generally called a quantum wire) and a three-dimensional quantum well structure (generally called a quantum box or a quantum dot), the carrier has one and zero degrees of freedom, respectively. Thus, it is called a one-dimensional carrier gas and a zero-dimensional carrier gas, respectively. In the multidimensional quantum well structure, the development of a laser diode with narrower spectra and lower threshold is forecasted, because the distribution of the density of the states for the carrier is different from that of the one-dimensional quantum well structure. Details, may be found in the publications by (1) Arakawa and A. Yariv, IEEE J. Quantum Electron QE-22, 1887 (1986) and (2) M. Asada, Y. Miyamoto, and Y. Suematsu, IEEE J. Quantum Electron, QE-22, 1915 (1986).
Furthermore, in the two-dimensional quantum well (quantum wire), high electron (hole) mobility brought about by the simplification of the scattering mechanism is predicted, and the development of a high performance electronic device is expected. Examples may be found in the publication H. Sakaki, Jpn. J. Appl. Phys. Vol. 19, L735 (1980).
Several methods for fabricating a multidimensional quantum well structure have been proposed. The publication by H. Temkin, G. J. Dolan, M. B. Panish, and S. N. G. Chu, Appl. Phys. Lett. Vol. 50, 413 (1987) discloses a combination of lithography and physical and chemical etching. In addition, the publication by T. Fukui, S. Ando, Y. Tokura, and T. Toriyama, Appl. Phys. Lett. Vol. 58, 2018 (1991) discloses a selective method of growing a crystal face. The publication by F. Wakaya, T. Kakuta, Y. Takagaki, Y. Yuba, S. Takaoka, K. Murase, T. Shiokawa, K. Gamo, and S. Namba, in J. Vac. Sci. Technol. Vol. B8, 1794 (1990) discloses a method of modulating a structure by means of an electric field. The publication by Y. Hirayama, S. Tarucha, Y. Suzuki, and H. Okamoto, in Phys. Rev. Vol. B37, 2774 (1988) propose a method for keeping a GaAs region as a quantum wire by alloying the ion-implanted region, using a thermal treatment of the irradiated area in which a Ga focused ion beam (FIB) is directed onto the GaAs--AlGaAs quantum well structure in a striped pattern. However, those methods have the disadvantages of requiring many processes and of being complicated. Moreover, a desired region cannot be fabricated with accurate dimensions because of the limitations of etching technology. Furthermore, in the method shown in Japanese patent document JA PUPA No. 62-134978, there is a problem that part of the crystal is damaged even in the region remaining as a quantum wire, because the portions in which the ions are implanted by using FIB and the portions around it generally sustain widespread irradiation damage.
In JA PUPA No. 62-134978, a method is disclosed drawing a carrier supply region first by maskless ion implantation and then by growing a crystal layer on that region and generating a carrier gas in that layer. However, in this method it is difficult to grow a high-quality crystal layer on a crystal damaged by ion implantation. It is thought that this layer would influence the performance of a semiconductor device to be fabricated. In addition, the above publication does not disclose a method for generating a zero- or one-dimensional carrier gas.